title: Interaction with damaged vessel wall in vivo in humans induces platelets to express CD40L resulting in endothelial activation with no effect of aspirin intake.
abstract: Activated platelets express CD40L on their plasma membrane and release the soluble fragment sCD40L. The interaction between platelet surface CD40L and endothelial cell CD40 leads to the activation of endothelium contributing to atherothrombosis. Few studies have directly demonstrated an increased expression of platelet CD40L in conditions of in vivo platelet activation in humans, and no data are available on its relevance for endothelial activation. We aimed to assess whether platelets activated in vivo at a localized site of vascular injury in humans express CD40L and release sCD40L, whether the level of platelet CD40L expression attained in vivo is sufficient to induce endothelial activation, and whether platelet CD40L expression is inhibited by aspirin intake. We used the skin-bleeding-time test as a model to study the interaction between platelets and a damaged vessel wall by measuring CD40L in the blood emerging from a skin wound in vivo in healthy volunteers. In some experiments, shed blood was analyzed before and 1 h after the intake of 500 mg of aspirin. Platelets from the bleeding-time blood express CD40L and release soluble sCD40L, in a time-dependent way. In vivo platelet CD40L expression was mild but sufficient to induce VCAM-1 expression and IL-8 secretion in coincubation experiments with cultured human endothelial cells. Moreover, platelets recovered from the bleeding-time blood activated endothelial cells; an anti-CD40L antibody blocked this effect. On the contrary, the amount of sCD40L released by activated platelets at a localized site of vascular injury did not reach the concentrations required to induce endothelial cell activation. Soluble monocyte chemoattractant protein-1, a marker of endothelium activation, was increased in shed blood and correlated with platelet CD40L expression. Aspirin intake did not inhibit CD40L expression by platelets in vivo. We concluded that CD40L expressed by platelets in vivo in humans upon contact with a damaged vessel wall activates endothelium; aspirin treatment does not inhibit this mechanism.
authors.affiliation: Div. of Internal and Cardiovascular Medicine, Dept. of Internal Medicine, Univ. of Perugia, Via E. dal Pozzo, 06126 Perugia, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Giannini
authors.forename: Emanuela
authors.initials: E
authors.lastname: Falcinelli
authors.forename: Loredana
authors.initials: L
authors.lastname: Bury
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Guglielmini
authors.forename: Roberta
authors.initials: R
authors.lastname: Rossi
authors.forename: Stefania
authors.initials: S
authors.lastname: Momi
authors.forename: Paolo
authors.initials: P
authors.lastname: Gresele
mesh_terms: D000328:Adult; D001241:Aspirin / Q000494:pharmacology* / Q000627:therapeutic use; D050197:Atherosclerosis / Q000503:physiopathology / Q000517:prevention & control; D001792:Blood Platelets / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D023201:CD40 Ligand / Q000378:metabolism*; D002450:Cell Communication / Q000502:physiology*; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology* / Q000293:injuries* / Q000503:physiopathology; D005260:Female; D006801:Humans; D007249:Inflammation / Q000503:physiopathology; D016209:Interleukin-8 / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D012867:Skin / Q000293:injuries; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
chemical_list: C111835:CCL2 protein, human; D018932:Chemokine CCL2; D016209:Interleukin-8; D010975:Platelet Aggregation Inhibitors; D019010:Vascular Cell Adhesion Molecule-1; D023201:CD40 Ligand; D001241:Aspirin